The present invention relates to a method and a device for regulating the speed of a motor vehicle and the distance of a motor vehicle from at least one motor vehicle driving ahead during a docking operation, the motor vehicle having a greater driving speed than the preceding motor vehicle.
It is conventional from the methods for automatic ranging (ADR) that at least speed v of the vehicle, relative velocity Vrel and distance sactual from the preceding vehicle are determined with the help of a detection device having a distance sensor. Moreover, the value of a normal acceleration an is calculated for braking of the vehicle as a function of the difference between a predefined standard setpoint trailing distance sn and distance sactual and of relative velocity Vrel. The vehicle is then braked at the normal acceleration, which is negative for a deceleration, in order to regulate the vehicle to standard setpoint trailing distance sn.
However, if the relative velocity of the two vehicles is too high, the braking effect exerted by the automatic ranging system is not sufficient to prevent the an insufficient setpoint trailing distance, i.e., the safety distance, or even a rear-end collision. The driver is then forced to actively intervene and trigger a greater braking effect. This problem arises particularly when the controlled variables for the automatic ranging system are set to a relatively large standard setpoint trailing distance sn and to low values for reliable normal accelerations an.
Such a method is described in European Published Patent Application No. 0 846 587, in which the distances to an object detected in front of the motor vehicle is detected by a distance sensor and is supplied to a control device, which forms one or more controlled variables at least as a function of a setpoint distance from a detected object determined at least from the instantaneous driving speed and/or of a predefined setpoint speed to adjust the driving speed of the motor vehicle.
Furthermore, a control device for maintaining a safety distance for a motor vehicle is described in U.S. Pat. No. 5,165,497 that sets the safety distance between the motor vehicle and the preceding motor vehicle in a speed range of 0 to 120 km/h in order to prevent a collision. The control performed by the control device goes so far that when the preceding vehicle stops, the vehicle is decelerated to a standstill. If the preceding vehicle then starts again, the vehicle also starts again. Consequently, there is a coupling between the vehicles, significant acceleration changes resulting in less comfortable handling properties being able to occur.
It is an object of the present invention to improve the functioning method of the method of this type as well as of the corresponding device and to facilitate more operator-friendly handling properties during the docking operation between two motor vehicles.
The above and other beneficial objects of the present invention are achieved by providing a method and device as described herein.
In a method according to the present invention, the value of a limiting acceleration ag is calculated for a deceleration of the vehicle as a function of the difference between a predefined setpoint limiting trailing distance sg and distance sactual and relative velocity Vrel, the value of the two values of normal acceleration an and of limiting acceleration ag having the greater magnitude is determined as braking acceleration ab to be used, and the vehicle is decelerated using a braking acceleration ab. In this context, limiting acceleration ag and setpoint limiting trailing distance sg represent parameters that for automatic ranging are at a setpoint trailing distance at the bottom limit or at an acceleration values to be used at the top limit for automatic ranging. The smallest setpoint trailing distance or safety distance corresponds to a trailing time of about 0.9 seconds, i.e., at every speed, the vehicle is to follow the preceding vehicle at a time interval of at least 0.9 seconds. However, the terms normal acceleration an and standard setpoint trailing distance sn represent parameters deviating from the previously described limiting values and corresponding to an automatic ranging system having a greater safety distance and lower maximum acceleration values.
It is recognized that the above described problematic driving situation in which the relative velocity of the two motor vehicles is not sufficient for the set xe2x80x9cnormalxe2x80x9d automatic ranging is able to be at least partially detected in that limiting acceleration ag is calculated in parallel with normal acceleration an and in that limiting acceleration ag is used when a deceleration of the motor vehicle at normal acceleration an is not sufficient for docking the vehicle. In this context, the driver of the motor vehicle is not prevented in every case from intervening. However, more significant braking than for normal automatic distance ranging increases the range of driving situations that are able to be controlled by the automatic distance ranging system in a comfortable manner without the intervention of the driver.
The magnitude of normal acceleration an and/or of limiting acceleration ag may increase as relative velocity Vrel increases or as distance sactual decreases. This means that when relative velocity Vrel is large, the automatic ranging system generates greater acceleration values than is the case for smaller values of relative velocity Vrel. The same is true for the situation in which distance sactual between both motor vehicles is small. If in this context the value of limiting acceleration ag increases more significantly than the value of normal acceleration an, the method according to the present invention begins at or above the parameters relative velocity Vrel and distance sactual as limiting acceleration ag is greater than normal acceleration an.
Normal acceleration an may be calculated with the help of a proportionality controller using a characteristics map using two input variables, e.g., relative velocity Vrel and the difference between standard setpoint trailing distance sn and actual distance sactual. Limiting acceleration ag may be calculated with the help of a proportionality controller using a characteristics map using two input variables, e.g., relative velocity Vrel and the difference between setpoint limiting trailing distance sg and actual distance sactual. A more precise mathematical description of an example embodiment is explained in the following on the basis of the description of the drawing.
Standard setpoint trailing distance sn may be calculated from speed v of the motor vehicle and a predefined standard trailing time tn. Setpoint limiting trailing distance sg may also be calculated from speed v of the motor vehicle and a predefined limiting trailing time tg. Limiting trailing time tg described above may have a value of about 0.9 seconds. In comparison, typical values for standard trailing time tn are in the range of 0.9 to 4.0 seconds, e.g., up to 2.0 seconds. Since an adjustment of the trailing time by the driver is intuitive, this refinement of the adjustment of the trailing distance is often used with the help of a trailing time.
The time characteristic of braking acceleration ab of the motor vehicle may be constant during the transition between normal acceleration an and limiting acceleration ag, i.e., there may be no abrupt change between the two acceleration values. This further increases the comfort of the automatic ranging system since there is no jolt in the movement of the vehicle.
The foregoing object may be achieved in accordance with the present invention by providing a device as described herein. This device is explained below in detail, with reference to an example, reference being made to the Figures.